Studies of the microsomal electron transport system responsible for the oxidative metabolism of many drugs has revealed the complexity of the pattern of regulation resulting from the stoichiometry of the requisite electron carrier enzymes and the limitation imposed by association of these enzymes with a membrane. Measurements of the kinetics of cytochrome P-450 reduction under a variety of conditions point to the role of membrane fluidity and alterations in the rate limiting step of the reaction sequence as major factors dictating the rate of drug metabolism. Associated studies of drug interaction with cytochrome P-450, hydrogen peroxide generation as an indicator of active oxygen, product adduct formation, and evaluation of endogenous substrate effects all characterize the potential multiple sites of control of this enzyme system. Comparative studies have been carried out using enzymes from liver, kidney, lung, and adrenal cortex. These comparative studies involve the purification of microsomal constituents, particularly from liver and kidney, and reconstitution of monooxygenase activities in the presence of phospholipids or in phospholipid vesicles. In addition, immunohistochemical experiments involving the use of fluorescein- and ferritin-labeled antibodies are being performed to determine the cellular and subcellular loci for these microsomal systems. The specific aims of this research program are to further our understanding of the molecular events associated with cytochrome P-450 function during drug metabolism as well as the biochemical evaluation of the perturbation of drug metabolism in vitro and in vivo.